Many prior art bike transmission systems use a shifter and derailleur combination that requires the shifter to hold tension on the derailleur by means of a large cable. In these prior art designs, the derailleur is controlled by a single cable from the shifter, requiring the derailleur to incorporate a large spring that is able to pull against the shifter, allowing the shifter to act as if it is pulling the derailleur back and forth between a plurality of gears, typically provided in a stacked arrangement known as a cassette. The shifter on these prior art designs is used to index the derailleur from gear to gear and contains complicated indexing components that help to align the derailleur as accurately as possible. Not only does this create a bulky, heavy and expensive shifter, but it also requires this added bulk to be mounted to handlebars, where aerodynamics are of concern.
By way of example, various known derailleur systems include U.S. Pat. No. 7,381,142 to Campagnolo, U.S. Pat. No. 4,437,848 to Shimano, U.S. Pat. No. 5,688,200 to White, and U.S. Pat. No. 4,183,255 to Leiter, all of which are hereby incorporated by reference in their entireties.
A significant problem with these prior art designs is that the cable is always under tension and as a result, the cable has the ability and tendency to stretch. When cable stretch occurs, which is common, the derailleur falls out of alignment with the sprockets, creating an undesirable shift, lowering efficiency, and in many cases, preventing the derailleur from shifting to the desired gear entirely. It is also difficult for prior art designs to perfectly align the derailleur with each sprocket due to the aforementioned cable slack issue as well as the fact that the prior art device used to regulate the accuracy of the derailleur is located almost two meters away from the system.
Cable slack in prior art designs is such a common problem that the designs have many adjustments incorporated into both the shifter and the derailleur to account for the issue. In addition, these prior art designs contain a chain slack device that is not only inefficient, but prevents the derailleur from functioning on sprockets that are over 36 teeth. On sprockets larger than 36 teeth, the chain slack arm is too close to the tire and ground to operate properly.